spi: zynq-qspi: Keep the bitfields naming consistent

spi: zynq-qspi: Keep the bitfields naming consistent

Most of the bits/bitfields #define'd in this driver are composed with:
1/ the driver prefix
2/ the name of the register they apply to

Keep the naming consistent by applying this rule to the CONFIG register
internals. These definitions will be used in a following change set.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20191108140744.1734-4-miquel.raynal@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>